The present invention relates to increasing blast temperatures, and more specifically to a method of using a plasma generator to increase the blast temperature in a shaft furnace for melting and possible reduction of metals and/or metal oxides.
It has long been known that by increasing the blast temperature in a blast-furnace it is possible to reduce the coke consumption and at the same time increase production. Furthermore, at blast temperatures above 850.degree. C., oil can be injected in tuyeres, thus achieving an additional saving in coke. The yield coefficient for oil is about 2 kg coke/kg oil for the first addition of oil. However, when more oil is added and constant blast temperature is maintained, this yield coefficient falls to a value of about 1 kg coke/kg oil. No further increase of the oil quantity is possible above a certain quantity since the combustion temperature in front of the tuyeres would be too low, and this would in any case entail reduced production.
These factors prompted attempts to increase the blast temperature as much as possible. However, increased blast temperature also enables the injection of fuels other than oil, such as coal dust or coke breeze, slurries of coal or coke in oil or water, natural gas, gas from coking plants, etc. Other additives can also be used at high blast temperatures, such as oxidic material e.g. water, iron ore, flue-gas dust are prereduced iron oxides as well as slag-formers.
An effective way of achieving the desired increase in blast temperature is to utilize the PLASMABLAST.RTM. method, according to which part or all the blast air is led through a plasma.
However, there are certain drawbacks entailed with this method in that the tuyeres often collapse for inexplicable reasons.
The object of the present invention is thus to eliminate the drawbacks of this known method.